Think of it as the school doors opening to let the kids out to go and play. It's is just a way of saying school is over, either for the day or a longer period like the summer vacation. School is finished for the day (or term or year) is another way to say the same thing. I hope that helps.

Could you provide a full sentence? It's unclear what you mean.

Yes, "let out" is commonly used, especially in casual conversation, to describe the time when schools finish for the day or when students are dismissed. Here are some alternative ways to say "schools let out": "Schools dismiss..." "School ends..." "Classes finish..." "The school day ends..." "Students are released..." Each of these can be used depending on the context, and they all convey a similar meaning.

Another way to say "schools let out" is "schools dismiss" or "schools end." "Let out" is commonly used in casual conversation to refer to the time when students are released from school for the day.

There's a few ways to say this: "School lets out at 4" "School gets out at 4" "School ends at 4" All of these work, but probably are more common in different regions. I live in California, and "School gets out at 4" is pretty common. "School lets out at 4" is correct, but also feels a little more stiff and formal, like you're stating a technical fact.